Pozzolanic activity of fly ash

Fly ash (FA) is finely divided by-product precipitated electrostatically from the combustion of pulverized coal in the thermal power plants. The hydration of four mixes of fly ash-lime 90:10, 80:20, 70:30 and 60:40 mass\% denoted as I.1, I.2, I.3 and I.4 was studied. Free lime, insoluble residue and combined water contents were determined up to 90 days. Phase composition and hydration products were investigated using DTA and FT-IR infrared spectroscopy. The change of electrical conductivity was also followed to monitoring the initial setting during the first 24 hours of hydration. The results revealed that the combined water content increases with the lime content especially after 7 days up to 90 days. DTA illustrates the formation of C-S-H, CAH and CASH hydrates. It is concluded that FA has a slightly pozzolanic activity and may be used in low cost filled pozzolanic cements.